Our climate is rapidly warming with rising temperatures impacting the physical environments that support entire ecosystems. Humans and fauna species alike face daunting challenges for survival because of climate change. The prospect isn’t lost on NUS climate change ecologist Assistant Professor Luo Xiangzhong. For him, childhood admirations for the works of early nature philosophers such as German naturalist Alexander von Humboldt, paired with a desire to tackle the climate change issue, introduced him to the world of climate change ecology.
A PhD trip to an eddy covariance tower in a Canadian forest sealed the deal. There, gazing at the colourful autumn canopies, he realised the tower was monitoring something invisible – the amount of water and carbon dioxide the forest was using and absorbing. The knowledge that the forest’s carbon dioxide uptake had risen for 10 years for reasons yet unknown crystallised his interest in the links between the visible and invisible, and how climate may impact ecosystems in ways we cannot directly see.
A recent study he led illustrates this relationship clearly. The study found that the amount of carbon dioxide taken in by land ecosystems, such as forests, could be linked to the availability of water, which is in short supply during droughts. This highlighted the significant impact droughts have on forests’ ability to take in carbon dioxide (or CO2) – the main greenhouse gas driving climate change – from the atmosphere.
We sat down recently with the Faculty of Arts and Social Sciences geographer to learn more about the importance of climate change ecology, its sister issues of carbon cycle and global photosynthesis, as well as his research.
What is climate change ecology?
Asst Prof Luo: Climate change ecology studies the interactions between climate change and natural ecosystems. This is a two-way process. On one hand, climate change influences ecosystems, leading to questions such as whether rising temperatures and reduced rainfall can make rainforests collapse. On the other hand, ecosystems can impact the climate through modulating carbon and water cycles on Earth. For example, ecosystems can mitigate global warming by taking CO2 out of the atmosphere through photosynthesis. Numerous environmental interactions and feedbacks cascade into a rather complex relationship between terrestrial ecosystems and climate change.
When we talk about ecosystems, we often think about trees and leaves. However, the advances in earth observation techniques in the past 20 years, such as eddy covariance, leaf gas exchange and earth system modelling, have helped us see way beyond that. It also presents a great opportunity for us to push the boundaries of knowledge and better understand ecosystem dynamics.
Could you share more details of your recent study on the link between droughts and forests’ ability to absorb carbon dioxide?
Asst Prof Luo: Ecosystems take up different amounts of CO2 from the atmosphere yearly and this leads to variations in the atmospheric CO2 concentration (e.g., when land ecosystems take up more CO2, the CO2 concentration level in the atmosphere grows slower). Scientists have been discussing the reason for the variations in ecosystem CO2 uptake and atmospheric CO2 concentration level, and have provided rather contrasting explanations – some suggest temperature anomalies are the main reason, some suggest soil moisture, others point to historical land-use changes.
In this study, we looked into the magnitude change of the variation over the past 60 years, and found a dominant role tropical extreme droughts played in modulating the atmospheric CO2 variation. This new discovery advances our understanding of the global carbon cycle, and highlights how tropical droughts, previously neglected and poorly considered in climate and carbon models, have in fact modulated the long-term variation in atmospheric CO2. As extreme droughts happen, ecosystems experience downregulation of photosynthesis, as well as tree mortality, fire, regeneration and deadwood decomposition. These processes would make the ecosystem CO2 uptake more variable in the long term. In particular, we found that droughts in tropical Asia ecosystems have outsized impacts on the long-term variation of the global carbon cycle, which will motivate our future studies to examine drought impacts on tropical Asia ecosystems, including those in Singapore.